We Keep Coding

How to convert Sting into instant in Java [duplicate]

This question already has answers here:
DateTimeParse Exception
(2 answers)
IST mapped to wrong ZoneId in java.time library
(3 answers)
Closed 5 months ago.
How to convert this string into instant:
String date = "Fri Sep 30 00:00:00 IST 2022";
Exception:
java.time.format.DateTimeParseException: Text 'Fri Sep 30 00:00:00 IST 2022' could not be parsed at index 0
at java.base/java.time.format.DateTimeFormatter.parseResolved0(DateTimeFormatter.java:2046)
at java.base/java.time.format.DateTimeFormatter.parse(DateTimeFormatter.java:1948)
at java.base/java.time.LocalDate.parse(LocalDate.java:428)
In DB it is saved in this format
ISODate("2022-09-29T18:30:00.000Z")
But while debugging in IDE it is coming in string format like this: "Fri Sep 30 00:00:00 IST 2022"
Now I want to convert it back to instant
I tried in this way:
DateTimeFormatter DATE_FORMAT_RULE = DateTimeFormatter.ofPattern("MM/dd/yyyy");
String date = "Fri Sep 30 00:00:00 IST 2022";
Instant instant = LocalDate.parse(date, DATE_FORMAT_RULE)
.atStartOfDay()
.toInstant(ZoneOffset.UTC);

The pattern you are using does not match the one of the String. Your pattern cannot parse a two-digit month first because the String starts with an abbreviated day of week, whose abbreviation even depends on the Locale, which you haven't specified, so it will take the system default.
However, you can try to parse it with a different pattern, but I don't think it will get you the desired result… Try DateTimeFormatter.ofPattern("EEE MMM dd HH:mm:ss z uuuu", Locale.ENGLISH) instead of your DateTimeFormatter.ofPattern("MM/dd/yyyy") and see the result. On my machine, it assumes IST to be Iceland Standard Time!
See this example:
public static void main(String[] args) {
// example String
String toBeParsed = "Fri Sep 30 00:00:00 IST 2022";
// first formatter: tries to parse "IST" as ZONE TEXT
DateTimeFormatter dtfZ = new DateTimeFormatterBuilder()
.appendPattern("EEE MMM dd HH:mm:ss")
.appendLiteral(' ')
.appendZoneText(TextStyle.SHORT)
.appendLiteral(' ')
.appendPattern("uuuu")
.toFormatter(Locale.ENGLISH);
// second formatter: tries to parse "IST" as ZONE NAME
DateTimeFormatter dtfz = DateTimeFormatter.ofPattern(
"EEE MMM dd HH:mm:ss z uuuu",
Locale.ENGLISH
);
// parse to a ZonedDateTime with the first formatter
ZonedDateTime zdt = ZonedDateTime.parse(toBeParsed, dtfZ);
// print the result
System.out.println("ZonedDateTime: "
+ zdt.format(DateTimeFormatter.ISO_ZONED_DATE_TIME));
// parse to a ZonedDateTime with the second formatter
ZonedDateTime zdt2 = ZonedDateTime.parse(toBeParsed, dtfz);
// print that, too
System.out.println("ZonedDateTime: "
+ zdt2.format(DateTimeFormatter.ISO_ZONED_DATE_TIME));
// convert to an Instant
Instant instant = zdt.toInstant();
// print the epoch millis
System.out.println(instant.toEpochMilli());
}
Output:
ZonedDateTime: 2022-09-30T00:00:00Z[Atlantic/Reykjavik]
ZonedDateTime: 2022-09-30T00:00:00Z[Atlantic/Reykjavik]
1664496000000
If you want the LocalDate.atStartOfDay(), you could simply extract it by calling toLocalDate() on an instance of ZonedDateTime (in case that ZonedDateTime contains any time of day different from zero hours, minutes, seconds and further down the units).

Corresponding to 2022-09-29T18:30:00.000Z, the IST in Fri Sep 30 00:00:00 IST 2022 refers to Indian Standard Time which has a time offset of UTC+05:30. You can build a formatter using .appendZoneText(TextStyle.SHORT, Set.of(ZoneId.of("Asia/Kolkata"))) with DateTimeFormatterBuilder as shown in the demo below:
public class Main {
public static void main(String[] args) {
DateTimeFormatter formatter = new DateTimeFormatterBuilder()
.appendPattern("EEE MMM dd HH:mm:ss")
.appendLiteral(' ')
.appendZoneText(TextStyle.SHORT, Set.of(ZoneId.of("Asia/Kolkata")))
.appendLiteral(' ')
.appendPattern("uuuu")
.toFormatter(Locale.ENGLISH);
Instant instant = ZonedDateTime.parse("Fri Sep 30 00:00:00 IST 2022", formatter).toInstant();
System.out.println(instant);
}
}
Output:
2022-09-29T18:30:00Z
Learn more about the the modern date-time API from Trail: Date Time.

Works for me
DateTimeFormatter DATE_FORMAT_RULE = DateTimeFormatter.ofPattern("E MMM dd hh:mm:ss z yyyy", Locale.US);
String date = "Fri Sep 30 00:00:00 IST 2022";
Instant instant2 = LocalDate.parse(date, DATE_FORMAT_RULE)
.atStartOfDay()
.toInstant(ZoneOffset.UTC);

Java DateTimeFormatter: DateTimeParseException with GMT-date

I would like to parse an GMT-date like Wed, 21 Oct 2016 07:28:00 GMTwith DateTimeFormatter into an Instant. To create the pattern i used the official documentation: DateTimeFormatter
My code so far:
String date = "Wed, 21 Oct 2016 07:28:00 GMT";
DateTimeFormatter gmtFormat = DateTimeFormatter.ofPattern("EEE' dd LLL yyyy HH:mm:ss '''");
TemporalAccessor parsed = gmtFormat.parse(date);
Instant a = Instant.from(parsed);
System.out.println(a);
But every time i've got this error:
Exception in thread "main" java.time.format.DateTimeParseException: Text 'Wed, 21 Oct 2016 07:28:00 GMT' could not be parsed at index 0
at java.time.format.DateTimeFormatter.parseResolved0(DateTimeFormatter.java:1949)
at java.time.format.DateTimeFormatter.parse(DateTimeFormatter.java:1777)
At index 0 is Wed, I used EEE which represents day-of-week by definition, there are also examples which represent: Tue; Tuesday; T.
I've also tried lower-, and uppercase but not successfully. What is wrong? Did I overlook something?

It works with the code
String date = "Fri, 21 Oct 2016 07:28:00 GMT";
DateTimeFormatter gmtFormat = DateTimeFormatter.RFC_1123_DATE_TIME;
TemporalAccessor parsed = gmtFormat.parse(date);
Instant a = Instant.from(parsed);
System.out.println(a);
But you have to change the day because otherwise it doesn't fit to the given date.

EEE is the proper format for Wed. But it does not include the comma.
Try this:
DateTimeFormatter gmtFormat = DateTimeFormatter.ofPattern("EEE, dd MMM yyyy HH:mm:ss '''");
Useful link

You're asking for redundant information: The day of the week and the date.
Change the format to just ignore the first three characters, leaving it reading the day/month/year.

Old Date Formatting incompatible with Java 8 ZonedDateTime API

I am updating my old date formatting code to Java 8 and trying the ZonedDateTime API.
The format of date is same as the Javascript Date object format, e.g. -
Thu May 25 2017 10:00:00 GMT+1200 (New Zealand Standard Time)
I was using the below format previously -
EEE MMM dd yyyy hh:mm:ss 'GMT'Z '('zzzz')'
This format fails to parse the date string using DateTimeFormatter.ofPattern method.
Here's the code:
public static final String DATE_FORMAT = "EEE MMM dd yyyy hh:mm:ss 'GMT'Z '('zzzz')'";
public static void main(String[] args) throws ParseException {
String sDate = "Thu May 25 2017 10:00:00 GMT+1200 (New Zealand Standard Time)";
parseDate(sDate);
}
private static void parseDate(String sDate) throws ParseException {
// works
DateFormat dateFormat = new SimpleDateFormat(DATE_FORMAT);
Date oldDate = dateFormat.parse(sDate);
//FIXME: can't parse?!
ZonedDateTime newDate = ZonedDateTime.parse(
sDate, DateTimeFormatter.ofPattern(DATE_FORMAT)); // <- this is the line 25!
}
Here's my full code for reference that can be compiled and run - https://gist.github.com/bhabanism/470e03db54981ad6ddedbba316dcaa9a
This fails at line#25 with:
Exception in thread "main" java.time.format.DateTimeParseException:
Text 'Thu May 25 2017 10:00:00 GMT+1200 (New Zealand Standard Time)'
could not be parsed: Unable to obtain ZonedDateTime from
TemporalAccessor: {HourOfAmPm=10, MilliOfSecond=0, MinuteOfHour=0,
OffsetSeconds=43200, MicroOfSecond=0, NanoOfSecond=0,
SecondOfMinute=0},ISO,Pacific/Auckland resolved to 2017-05-25 of type
java.time.format.Parsed
Note, I can't change the input format of the Date, it has to be
Thu May 25 2017 10:00:00 GMT+1200 (New Zealand Standard Time)
I can surely modify the formatter
EEE MMM dd yyyy hh:mm:ss 'GMT'Z '('zzzz')'

It seems there was a bug in your format string all the time. Lowercase hh is for hour within AM or PM, in the range 1 through 12. Since you don’t have AM/PM in your string, I suspect this was never what you wanted, and I wonder how the error went unnoticed.
Uppercase HH is for hour of day, 0 through 23:
public static final String DATE_FORMAT = "EEE MMM dd yyyy HH:mm:ss 'GMT'Z '('zzzz')'";
With this change both the old and the new way of parsing works on my computer.
When adding Locale.ENGLISH to both formatters, that is. You may want to do the same.
The results I get are
Thu May 25 00:00:00 CEST 2017
2017-05-25T10:00+12:00[Pacific/Auckland]
Since CEST is 2 hours ahead of UTC, this is the same point in time, only rendered differently.

Can't convert string to date in Java, wrong timezone after conversion

I have an array of Strings with the dates e.g.:
Tue, 09 Feb 2016 14:07:00 GMT;
Tue, 09 Feb 2016 19:55:00 GMT.
Now I want to find the most recent date on this list. In order to do that, I try to deserialize these strings to java.util.Date objects and after that compare them.
The code sample of java.util.Date object generation:
strDate = "Tue, 09 Feb 2016 14:07:00 GMT";
DateFormat format = new SimpleDateFormat("EEE, dd MMM yyyy HH:mm:ss z");
Date date;
try {
date = format.parse(strDate);
//Result: Tue Feb 09 16:07:00 IST 2016
System.out.println("Result: " + date.toString());
} catch(ParseException e) {
e.printStackTrace();
}
My questions:
Why is the result in IST 2016 time zone and not in GMT? What does the IST 2016 stand for? Is it India Standard Time or Irish Standard Time or Israel Standard Time?
The initial string is in EEE, dd MMM format, the SimpleDateFormat pattern is also in this format, thus, why the result is in EEE, MMM dd format?
How can get a java.util.Date object in the same timezone as the initial string, in my case — GMT?
Is the approach I'm using to find the most recent date in the list is OK or there is more convenient/modern way to do that in Java 8, e.g., with the usage of LocalDateTime?

You are relying to Date.toString() to print your date when you should format it to a String with a formatter. What you are seeing is just the default pattern of Date.toString(). What you must keep in mind is that a Date does not have a timezone. You are seeing the output with the IST timezone, this must be because the current locale for the JVM is set to some specific locale for which the timezone name is "IST".
With regard to your point 4, yes, you can do it much cleaner with Java Time API introduced in Java 8. You can create a List of your strings to parse, create a DateTimeFormatter to parse it, and keep the maximum date value.
public static void main(String[] args) {
List<String> dates = Arrays.asList("Tue, 09 Feb 2016 14:07:00 GMT", "Tue, 09 Feb 2016 19:55:00 GMT");
DateTimeFormatter formatter = DateTimeFormatter.ofPattern("EEE, dd MMM yyyy HH:mm:ss z", Locale.ENGLISH);
ZonedDateTime maxDate = dates.stream()
.map(s -> ZonedDateTime.parse(s, formatter))
.max(ZonedDateTime::compareTo)
.get(); // or .orElse(null)
System.out.println(maxDate);
}
This code is using a ZonedDateTime to keep the time-zone of the incoming strings.

Your computer seems to be set to IST. To force GMT output, import java.util.TimeZone and do this in your try block:
format.setTimeZone(TimeZone.getTimeZone("GMT"));
date = format.parse(strDate);
System.out.println("Result: " + format.format(date));

how to convert date in java

I am new in android .
I have to convert following date into this time stamp (Wed Oct 12 14:17:42 GMT+05:30 2011)
Thu, 27 May 2010 12:37:27 GMT
This is the date that I am getting from the server through the header. I have converted it into the String object. Now I have to convert it into the Date format like: Wed Oct 12 14:17:42 GMT+05:30 2011
Please could you help me how should I convert it into the (Wed Oct 12 14:17:42 GMT+05:30 2011) this format using timestamp.

Have a look at DateFormat or SimpleDateFormat which provide parse() and format() methods. DateFormat provides a bunch of standard formats whereas SimpleDateFormat allows you to provide your own format expression.
Example for your input date:
//note that you need the locale as well, since the weekdays and months are written in a specific language, English in that case
SimpleDateFormat parseFormat = new SimpleDateFormat( "E, dd MMM yyyy HH:mm:ss z", Locale.ENGLISH );
SimpleDateFormat writeFormat = new SimpleDateFormat( "E MMM dd HH:mm:ss z yyyy", Locale.ENGLISH );
writeFormat.setTimeZone( TimeZone.getTimeZone( "GMT" ) );
Date tDate = parseFormat.parse( "Wed, 12 Oct 2011 14:17:42 GMT" );
System.out.println(writeFormat.format(tDate )); //Wed Oct 12 14:17:42 GMT 2011
Edit: If you want a more usable API, try JodaTime.